The present invention relates to an ultrasonic motor in which piezoelectric vibrators are laminated in a body in the longitudinal direction in parallel to its polarizing direction land more particularly to an improvement of an ultrasonic motor utilizing longitudinal vibration of the piezoelectric vibrators and an electronic apparatus equipped with the ultrasonic motor.
An ultrasonic motor utilizing vibration of piezoelectric vibrators is drawing attention lately in the field of micromotors.
An ultrasonic motor utilizing stretching vibration and bending vibration of rectangular piezoelectric vibrators (dual-mode vibrator) in particular is used in various uses because it is capable of moving an object linearly or rotatably by combined vibration of those two vibrations. An ultrasonic motor of a type in which piezoelectric bodies are layered is also used a high output is required (see Japanese Patent Laid-Open No. Hei. 7-184382).
FIG. 16 shows an ultrasonic motor of a type in which rectangular plate-like piezoelectric bodies are layered. A basic vibrator of the ultrasonic motor comprises piezoelectric bodies 61, 62, 63, 64, 65 and 66 which are polarized in a predetermined manner so as to vibrate in the dual mode and are layered in the polarizing direction, output fetching members 71, 72, 73, 74, 75 and 76 provided on edge portions 61a, 62a, 63a, 64a, 65a and 66a provided in the direction vertical to the polarizing direction of the piezoelectric bodies 61 through 66, and electrodes (not shown) provided on both sides of the piezoelectric bodies 61 through 66. The six piezoelectric vibrators, i.e., the piezoelectric bodies of two rows arrayed in the horizontal direction and stacked in three layers in the vertical direction, are held by coupling means 67, 68 and 69.
When voltage is applied from the electrodes, the respective piezoelectric bodies 61 through 66 vibrate in the dual modes and the combined vibration thereof is transmitted to the respective output fetching members 71 through 76 to move an object abutting with the output fetching members 71 through 76.
It is designed to obtain a high output by taking out the output from the plurality of piezoelectric bodies 61 through 66.
However, because the respective piezoelectric bodies 61 through 66 are fixed merely by part thereof by the coupling means 67 through 69, the vibrating direction may vary among the respective piezoelectric bodies 61 through 66 in the ultrasonic motor described above. It also has had a technological problem that because the vibration of the fixed parts of the piezoelectric bodies 61 through 66 is suppressed, it causes vibration loss and the output cannot be taken out effectively.
Still more, it is not preferable to use the above-mentioned coupling means 67 through 69 as the separate members for fixing the respective piezoelectric bodies 61 through 66 because it enlarges and complicates the whole structure of the motor and because the production process thereof is complicated by adding the step for mounting the coupling means 67 through 69.
Meanwhile, although the above-mentioned problem may be solved by laminating the piezoelectric bodies in a body in the polarizing direction and by taking out the output only by the piezoelectric transverse effect, there is a technological problem that a high output cannot be obtained because the electric-mechanic coupling coefficient of the piezoelectric transverse effect is small.
Accordingly, it is an object of the present invention to solve the above-mentioned technological problems by providing an ultrasonic motor whose vibration loss is suppressed, whose structure is miniaturized, whose production process is simplified and which is capable of utilizing electrical energy efficiently.
It is another object of the present invention to provide an electronic apparatus equipped with an ultrasonic motor.
In order to achieve the above-mentioned objectives, an inventive ultrasonic motor comprises a first piezoelectric body having a first polarized portion excited when voltage is applied and a second piezoelectric body that is laminated with the first piezoelectric body in the longitudinal direction parallel to the polarizing direction. The second piezoelectric body has a first polarized portion at a position separated from the first polarized portion of the first piezoelectric body in the transverse direction vertical to the polarizing direction, and moves a moving body by stretching vibration and bending vibration caused by vibrations of the first polarized portion of the first piezoelectric body and the first polarized portion of the second piezoelectric body in the longitudinal direction.
The polarized portion of the first piezoelectric body and the polarized portion of the second piezoelectric body excite in the vertical and horizontal directions, respectively. The stretching vibration is then produced when the respective vibrations in the longitudinal direction overlap and the bending vibration is produced from the implication between the transverse vibrations and the stretching vibration therearound. The moving body is then moved by elliptic vibration obtained by combining the stretching vibration and the bending vibration.
Further, the piezoelectric vibrators are laminated in a body without using fixing means, so that the vibration is not suppressed and the vibrating direction is fixed.
Accordingly, the invention allows electrical energy to be utilized very efficiently by utilizing the longitudinal vibration caused by the piezoelectric longitudinal effect whose electrical-mechanical coupling coefficient is large, vibration loss to be suppressed, the vibrating direction to be prevented from varying, the structure of the device to be miniaturized and the production process to be simplified.
The invention is further characterized in that the first and second piezoelectric bodies have second polarized portions further at positions corresponding to the first polarized portions.
Thereby, elliptic vibration for rotating in the reverse direction may be taken out by exciting only the second polarized portions of the respective piezoelectric bodies to produce bending vibration having a different phase, for example. Alternatively, the bending vibration may be amplified by exciting the second polarized portion with a different phase from the first polarized portion in the same time. Accordingly, driving force in the both normal and reverse directions may be obtained and the output may be controlled by displacing the bending vibration or by changing the phase.
The invention is further characterized in that a third piezoelectric body which vibrates in the same phase with the stretching vibration is laminated in a body of the ultrasonic motor.
Thereby, the third piezoelectric body vibrates in the longitudinal direction in the same phase with the stretching vibration and amplifies the stretching vibration. Accordingly, the high-output ultrasonic motor may be realized.
The invention is further characterized in that a third polarized portion that vibrates in the same phase with the stretching vibration is provided between the first polarized portion of the first piezoelectric body and the first polarized portion of the second piezoelectric body at least in either one of the first piezoelectric body and the second piezoelectric body. Thereby, the third polarized portion vibrates in the longitudinal direction in the same phase with the stretching vibration and amplifies the stretching vibration. Accordingly, the high-output ultrasonic motor may be realized.
Here, the third polarized portion may be provided only in the first piezoelectric body, only in the second piezoelectric body or in the first and second piezoelectric bodies.
The invention described is further characterized in that the moving body of the ultrasonic motor is abutted to the laminated piezoelectric vibrator in the horizontal direction.
Thereby, the laminated piezoelectric vibrator moves the moving body by the vibration combined in the horizontal direction.
The invention is further characterized in that the laminated piezoelectric vibrator is abutted at least at one point of a spherical moving body of the ultrasonic motor described in any one of the foregoing embodiments.
Thereby, the spherical moving body may be moved about an arbitrary axis by applying a driving force to one point of the spherical moving body by the laminated piezoelectric vibrator or may be moved arbitrary by applying a driving force to a plurality of points.
The invention is further characterized in that an electronic apparatus equipped with the ultrasonic motor comprises the ultrasonic motor described in any one of the foregoing embodiments. Thereby, the electronic apparatus equipped with the ultrasonic motor having the ultrasonic motor as a driving source may be realized.
The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings in which like numerals refer to like parts.